Change "+towgs84" parameters in EPSG codes 5343 to 5349

[hguagni]

In some GIS software the following line "+ towgs84 = -0.41,0.46, -0.35,0,0,0,0" is recognized, but the transformation between POSGAR 2007 and WGS84 must be null ("+ towgs84 = 0,0,0,0,0,0,0").
These parameters were provided by YPF (calculated from the stations common to POSGAR 1994 and POSGAR 2007), but lead to user confusion and spatial compatibility issues when sharing data between different GIS applications.
This problem is reported in users who use QGIS in versions later than 3.10. Can you please modify or remove these parameters?
Thank you!

Hernán J. Guagni
Ingeniero Agrimensor

Jefe del Departamento Marcos de Referencia
Dirección de Geodesia
Instituto Geográfico Nacional - República Argentina
https://www.ign.gob.ar/

[rouault]

Candidate fix in #2357

This doesn't fix exactly as you suggest. From the EPSG database, there's no reason to select +towgs84=0,0,0,0,0,0 more than +towgs=#2357 . So as there are 2 candidates, do not choose any for the legacy PROJ.4 string.
But for QGIS, the main interesting change is that now QGIS will see 2 transformations, which will enable the user to choose the one he believes to be appropriate

That said when using PROJ automatic modes such as cs2cs, EPSG:9264 will continue to be used, because in the absence of other hints, it has the best accuracy.

[hguagni]

Even,
Thanks for the reply. I have exported the same vector entity from two different software, for example QGIS and Global Mapper (associating the EPSG code 5347 in both cases).
When importing the two shape files, the entities are automatically rendered incorrectly as you can see in the image (QGIS does not allow to choose any option).
How do the users achieve compatibility of the results in this case?

Hernán J. Guagni
Ingeniero Agrimensor

Jefe del Departamento Marcos de Referencia
Dirección de Geodesia
Instituto Geográfico Nacional - República Argentina
https://www.ign.gob.ar/

[rouault]

When importing the two shape files, the entities are automatically rendered incorrectly as you can see in the image (QGIS does not allow to choose any option).
How do the users achieve compatibility of the results in this case?

He, you are too impatient ! I explained I've just submitted a change for PROJ so that QGIS can now propose the 2 possible transformations to the user. You'll need to wait for QGIS to use the PROJ version (7.2) where the fix will land.

[hguagni]

Perfect Even! Thank you very much for your attention and apologies for the impatience (it was a confusion).
We write any news. Regards!